Increased use of light weight panels in aircraft construction has emphasized the need for an improved grommet that facilitates anchoring and/or the attachment of other components to such panels. Such panels generally comprise a honeycomb or structural foam core having fiber reinforced plastic or aluminum skins of approximately 0.010 to 0.030 of an inch in thickness on opposite sides thereof.
Known fasteners, grommets or anchorage devices exhibit certain disadvantages when utilized with relatively soft structural materials. For example, undesirable compressive loads are applied to such panels when a screw type fastener is advanced thereinto. Excessive compressive load may cause the plastic material of the panel to creep, substantially decreasing clamp load resulting in a loose, structurally compromised joint.
Other known fastening or anchorage proposals have incorporated sleeves or inserts with teeth or projections that are displaced outwardly from a supporting sleeve so as to dig or bite into the surrounding material. The disadvantage of such fasteners is that the resistance to axial pull-out provided by the teeth or other projections is often insufficient to maintain joint integrity. This disadvantage is greatly magnified when the sleeve or insert is utilized in soft materials such as structural foam where the density of the foam material decreases towards the center of the panel.